1. Field of the Invention
The present invention relates to a cylinder apparatus which has a cushion mechanism capable of changing the displacement speed of a piston around an end of displacement thereof. The piston is displaceable in the axial direction in a cylinder body.
2. Description of the Related Art
A cylinder apparatus driven by a pressure fluid is used as a driving mechanism for transporting and positioning a workpiece or driving a variety of industrial machines.
As shown in FIG. 8, the cylinder apparatus comprises a piston 2 which is provided displaceably in a cylinder body 1. An elongate piston rod 3 is connected to the piston 2. A head cover 4a and a rod cover 4b are connected to ends of the cylinder body 1, and the ends of the cylinder body 1 are closed thereby. Pressure fluid ports 5a, 5b, through which the pressure fluid is supplied and discharged, are formed in the head cover 4a and the rod cover 4b, respectively. The piston 2 is displaced in the axial direction by the pressure fluid supplied from the pressure fluid ports 5a, 5b to a cylinder chamber 6 in the cylinder body 1.
Cushion valves 7a, 7b are provided for the head cover 4a and the rod cover 4b, each of which controls the flow rate of the pressure fluid discharged from the cylinder chamber 6.
The head cover 4a and the rod cover 4b are provided with check valves 8a, 8b which are disposed in the vicinity of the cushion valves 7a, 7b. 
First communication passages 9a are formed so that the cylinder chambers 6 communicate with holes in which the cushion valves 7a, 7b are provided. The holes communicate with the interiors of the head cover 4a and the rod cover 4b into which the piston rod 3 is inserted.
Second communication passages 9b are formed so that the cylinder chambers 6 communicate with holes in which the check valves 8a, 8b are provided. The holes communicate with the interiors of the head cover 4a and the rod cover 4b into which the piston rod 3 is inserted.
The cushion valves 7a, 7b can be screwed by the screw sections with respect to the head cover 4a and the rod cover 4b. When the cushion valves 7a, 7b are screwed, the cushion valves 7a, 7b are displaced in the direction substantially perpendicular to the axis of the cylinder body 1. The cross-sectional areas of the flow passages for the pressure fluid flowing through the first communication passages 9a are changed by the ends of the cushion valves 7a, 7b when the cushion valves 7a, 7b are displaced to adjust the flow rates of the pressure fluid to be discharged to the outside from the pressure fluid ports 5a, 5b via the first communication passages 9a. 
When the pressure fluid is supplied from one pressure fluid port 5b near the rod cover 4b, for example, the piston 2 is displaced toward the head cover 4a together with the piston rod 3. During this process, the pressure fluid remaining in the cylinder chamber 6 disposed near the head cover 4a is discharged to the outside from the pressure fluid port 5a via the interior of the head cover 4a into which the end of the piston rod 3 is inserted when the piston 2 is displaced.
When the end of the piston rod 3 is inserted into the head cover 4a, the pressure fluid is discharged from the pressure fluid port 5a via the first communication passage 9a. The displacement speed of the piston 2 is decelerated by adjusting the discharge amounts of the pressure fluid flowing through the first communication passages 9a by screwing the cushion valves 7a, 7b as described above (see, for example, “JIS Handbook”, JIS B 8377-1981 (p. 538, FIG. 2)).
In the case of the cylinder apparatus disclosed in “JIS Handbook”, JIS B 8377-1981 (p. 538, FIG. 2), the flow rates of the pressure fluid to be discharged from the first communication passages 9a are adjusted by screwing the cushion valves 7a, 7b provided in the head cover 4a and the rod cover 4b, respectively, to change the displacement speed of the piston 2 which is displaced in the cylinder body 1. Thus, the piston 2 is prevented from the collision with the head cover 4a or the rod cover 4b by cushioning.
However, in the conventional apparatus, when the displacement speed of the piston 2 is adjusted by using the cushion valves 7a, 7b, the cushion valves 7a, 7b are displaced in the axial direction. Therefore, for example, the cushion valves 7a, 7b are recessed by predetermined depths from the side surface of the cylinder body 1. When the cylinder apparatus is used in an environment in which liquid or the like is used in the vicinity of the cylinder apparatus, the liquid and the dust or the like are remained in the holes in which the cushion valves 7a, 7b are installed.